I haven't been able to mess w any of my broodmares for the past 2 weeks, because of the holiday, but I finally brought them all up today. While I was grooming Tink (17yr old WH) I noticed this strange lump on her chest. It's on the left side of her chest. It's a hard lump and a little lower is what feels like a sac of fluid. I didn't feel any scabs and she didn't budge while I was messing with it. What could this be???